The present invention relates generally to magnetic remote control switches and more particularly to low voltage transformer relays.
A variety of magnetic remote control switches exist in the art. Some of these magnetic remote control switches incorporate a transformer along with an electromagnetic structure. Such a combination structure allows a switching system to be remotely controlled from low voltage switches connected to the secondary winding of the transformer. Typically these structures are then called low voltage transformer relays.
Two examples of low voltage transformer relays are described in U.S. Pat. No. 3,461,354, Bollmeier, Magnetic Remote Control Switch and U.S. Pat. No. 4,321,652, Baker et al, Low Voltage Transformer Relay. In both structures a transformer is provided within an electromagnetic structure. The transformer has a primary winding (coil) and a secondary winding (coil). The primary winding is connected to a source of alternating current, e.g., a 60 hertz power source. The electromagnetic structure contains an armature which is magnetically stable in either of two positions. The armature carries or activates a set of contacts which contains load carrying contacts. With the secondary winding of the transformer open, the electromagnetic device remains stable in its prior position. Bidirectional switches can be coupled in parallel, either directly or through an interface circuit, to the secondary winding of the electromagnetic device. The bidirectional switches can be activated to restrict the current flowing in the secondary winding to either a first or a second direction switching the transformer relay to either a first or a second position, thus operating the load carrying contacts.
A single such electromagnetic device, low voltage transformer relay, may be connected to a plurality of bidirectional switches. This connection operates fine as long as only one of the bidirectional switches is operated at any one time. However, if two, or more, bidirectional switches are simultaneously activated in opposite directions, the result is an effective short across the secondary winding of the low voltage transformer relay. With the primary winding of the low voltage transformer relay coupled to an alternating current power source, the low voltage transformer relay may switch following the waveform of the alternating current excitation power. With a positive excursion of the excitation power, the low voltage transformer relay would switch to a first position. With the next negative excusion of the excitation power, the transformer relay would switch to the second position. Again with the next positive excursion of the excitation power, the transformer relay would switch back to the first position. This resultant "chatter" is detrimental to the functioning of the low voltage transformer relay. If the excitation power is 60 hertz (common in the United States) the transformer relay would switch 120 times per second. Heat buildup caused by such rapid switching may well be detrimental to the low voltage transformer relay components in a relatively short time and may very well cause failure of the low voltage transformer relay within a few seconds of such operation.
There has been an electronic solution to the problem of low voltage transformer relay "chatter." U.S. patent application Ser. No. 332,145, Mosier, filed Dec. 18, 1981, is directed toward preventing such "chatter" by interfering with the ability of the bidirectional switch from creating an effective short across the secondary winding of the transformer relay.